Olefin metathesis has become an exceptionally powerful and applicable method for the formation of carbon-carbon bonds in organic and polymer synthesis. Ruthenium-based complexes (1-3) are the most commonly employed olefin metathesis catalysts in academic and industrial laboratories, because they can be handled in air and are tolerant of various organic functional groups.
(see (a) Schrodi, Y.; Pederson, R. L. Aldrichim. Acta 2007, 40, 45-52. (b) Grubbs, R. H. Adv. Synth. Catal. 2007, 349, 34-40). However, the syntheses of these complexes are relatively cumbersome, usually involving more than one step and requiring isolation of the catalysts to remove catalyst-inhibiting by-products such as liberated phosphine ligands (Scheme 1). (see, e.g., (a) Schwab, P.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc. 1996, 118, 100-110. (b) Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Org. Lett. 1999, 1, 953-956. (c) Chatterjee, A. K.; Morgan, J. P.; Scholl, M.; Grubbs, R. H., J. Am. Chem. Soc. 2000, 122, 3783-3784. (d) Kingsbury, J. S.; Harrity, J. P. A.; Bonitatebus, P. J., Jr.; Hoveyda, A. H., J. Am. Chem. Soc. 1999, 121 (4), 791-799. (e) Garber, S. B.; Kingsbury, J. S.; Gray, B. L.; Hoveyda, A. H. J. Am. Chem. Soc. 2000, 122, 8168-8179. (f) Fürstner, A.; Guth, O.; Duffels, A.; Seidel, G.; Liebl, M.; Gabor, B.; Mynott, R., Chem.-Eur. J. 2001, 7, 4811-4820. (g) Fürstner, A.; Thiel, O. R.; Ackermann, L.; Schanz, H.-J.; Nolan, S. P., J. Org. Chem. 2000, 65, 2204-2207. (h) Monsaert, S.; Drozdzak, R.; Dragutan, V.; Dragutan, I.; Verpoort, F., Eur. J. Inorg. Chem. 2008, 432-440).
Therefore, a one-step procedure that forms highly active olefin metathesis catalysts and does not require purification or isolation would provide certain advantages. Ideally, the new procedure should be as atom-economic as possible. In particular, a new method that requires only one equivalent of expensive ligands (e.g., PCy3) per ruthenium center would be desirable.
Previous attempts to generate olefin metathesis catalysts in situ focused on the preparation of ruthenium vinylidene (see (a) Katayama, H.; Ozawa, F., Coord. Chem. Rev. 2004, 248, 1703-1715. (b) Katayama, H.; Ozawa, F., Organometallics 1998, 17, 5190-5196. (c) Louie, J.; Grubbs, R. H., Angew. Chem., Int. Ed. 2001, 40, 247-249.) and allenylidene species (see (a) Dragutan, I.; Dragutan, V., Platinum Met. Rev. 2006, 50, 81-94. (b) Fürstner, A.; Liebl, M.; Lehmann, C. W.; Picquet, M.; Kunz, R.; Bruneau, C.; Touchard, D.; Dixneuf, P. H., Chem.-Eur. J. 2000, 6, 1847-1857. (c) Schanz, H.-J.; Jafarpour, L.; Stevens, E. D.; Nolan, S. P., Organometallics 1999, 18, 5187-5190). However, these types of complexes proved less active in olefin metathesis than their ruthenium-alkylidene counterparts. For example, ruthenium allenylidene complex 4 can be very conveniently prepared in a one-step procedure involving the treatment of [RuCl2(p-cymene)]2 with 1,1-diphenylprop-2-yn-1-ol in the presence of two equivalents of PCy3 (Scheme 2). (See Schanz, H.-J.; Jafarpour, L.; Stevens, E. D.; Nolan, S. P., Organometallics 1999, 18, 5187-5190). Unfortunately, 4 is inactive in olefin metathesis although its chemical isomer-ruthenium-indenylidene complex 3a-shows good activity. (See; and Schanz, H.-J.; Jafarpour, L.; Stevens, E. D.; Nolan, S. P., Organometallics 1999, 18, 5187-5190).

Recently the Schrodi and Bruneau groups have published interesting chelating indenylidene catalysts. (See Jimenez, L. R.; Gallon, B. J.; Schrodi, Y. Organometallics 2010, 29, 3471-3473, incorporated herein by reference, and Kabro, A.; Roisnel, T.; Fischmeister, C.; Bruneau, C. Chem.-Eur. J. 2010, 16, 12255-12261).
Despite the advances achieved in the preparation of olefin metathesis catalysts, a continuing need exists for new synthetic methods for preparing such catalysts. Of particular interest are methods that provide techniques for the preparation of new catalysts, while also providing for better utilization of reactants and improved product yields.